Continuous flow solid phase synthesis of various peptides and foldamers with exceptionally low amino acid consumption

The importance of synthesis of peptides and foldamers is warranted by the need for peptide-based medicines, the roles of peptides and foldamers in drug discovery, etc. Since its introduction by Merrifield, peptide synthesis was performed almost exclusively on solid supports. It has been applied for the synthesis of foldamers as well. The solid-phase peptide synthesis (SPPS) technique has subsequently been progressively developed. However, still a general property of these methodologies are the high number of amino acid equivalents required for total coupling.1 Continuous-flow (CF) approaches have recently gained in significance among synthetic techniques.2 We show here that the number of amino acid equivalents used for SPPS can be lowered drastically to around 1.5 equivalents through the application of a CF technique and by complete reaction parameter optimization. Under the optimized conditions the couplings of all 20 proteinogenic amino acids with 1.5 amino acid equivalents proceeded with excellent conversions. To demonstrate the efficiency of the CF-SPPS methodology, known difficult sequences were synthetized in automated way. As further evidence of the effectiveness, β-peptide foldamers with alicyclic side-chains.